The invention relates to a semiconductor device comprising a semiconductor body provided at a surface with a charge transfer device having an output stage, which comprises a read-out zone located at the surface and an amplifier having a feedback capacitor, an inverting input of the amplifier being connected to the read-out zone and an output of the amplifier being fed back through the capacitor to the input.
Such a semiconductor device is known from European Patent Application laid open to public inspection under No. 46,549. In the known device, a charge packet reaching the read-out zone is supplied to the feedback capacitor, as a result of which the voltage across the feedback capacitor varies. This voltage variation is a measure for the supplied quantity of charge. In analogous applications, a linear relation should exist between the quantity of supplied charge and the voltage variation across the capacitor in order to be able to determine in a simple manner the quantity of supplied charge from the voltage variation. For this purpose it is required that the capacitor has a voltage-independent capacitance. According to the said Application, a capacitor of the MOS type is not particularly suitable to this end because its capacitance depends upon the voltage across the capacitor.
Further, in general a capacitor can be formed in a semiconductor device by using a cut-off pn junction or two conductive layers between which a dielectric layer is disposed. Besides these capacitors integrated in the semiconductor device, a non-integrated capacitor may also be used. However, all these alternatives have disadvantages. For example, the capacitance of a cut-off junction is voltage-dependent, as a result of which the relation between the quantity of charge at the capacitor and the voltage read out across it is non-linear. The manufacture of the capacitor comprising two conductive layers and an intermediate dielectric layer often does not fit into existing processes and consequently would involve in many cases additional processing steps. The non-integrated capacitor has the disadvantage that it is comparatively expensive and moreover requires additional contact surfaces in the semiconductor device and in connection therewith additional connecting pins in the envelope.